The reduction-oxidation (redox) flow battery is an electrochemical storage device that stores energy in a chemical form and converts the stored chemical energy to an electrical form via spontaneous reverse redox reactions. Due to the decoupling of the electrolyte (energy capacity) from the stack (power module), a flow battery offers the ability to change energy storage capacity without altering the entire system, the ability to increase maximum power output with minimal system impact, as well as a reduction of part redundancy in comparison to other battery technologies. Hybrid flow batteries are distinguished by the deposit of one or more electro-active materials on an electrode. In hybrid battery systems, the energy stored by the redox battery may be limited by the amount of metal plated during charge and may accordingly be determined by the efficiency of the plating system as well as the available volume and surface area for plating.
The all-iron hybrid flow battery allows for the use of an inexpensive electrolyte material, such as FeCl2 (or FeSO4), wherein on the positive electrode each of two Fe2+ ions loses an electron to form Fe3+ during charge, while each of two Fe3+ ions gains an electron to form Fe2+ during discharge. On the negative electrode, Fe2+ ions receive two electrons and deposit as iron metal during charge, while iron metal loses two electrons and re-dissolves as Fe2+ during discharge:2Fe2+Fe3++2e− (Positive/Redox Electrode)Fe2++2e−Fe0 (Negative/Plating Electrode)
Hybrid flow batteries may use forced convection to pump redox electrolyte into a flow cell and across a redox plate, which conducts the electrolyte through channels allowing for redox reactions to occur at an adjacent redox electrode. The redox plate also allows for the removal of reacted electrochemical species away from the reaction sites. Forced convection ensures fresh, unreacted electrolyte to always be in contact with the electrode surface. Additionally, this configuration allows the entire electrode surface to be utilized, while simultaneously removing any products formed. The ferric/ferrous redox reaction occurs rapidly. As such, the redox plate design does not limit the performance of the IFB. However, by pumping electrolytes through graphite flow channels, unnecessary reactions may occur on both the surface of the channels and the surface of the electrode, leading to unnecessary ohmic losses. Further, an all-graphite or C/Graphite composite channels cannot be formed by inexpensive manufacturing methods such as injection molding.
The plating reaction at the negative electrode is the primary source of the IFB performance loss, as a result of the plating kinetics, resistance, and mass transport losses. For an all-iron hybrid flow battery, the battery capacity depends on the amount of solid iron that can be deposited at the negative electrode. Limited plating surface area thus results in higher overpotential on the negative electrode in order for the reaction to occur, while a limited plating volume may limit the overall battery capacity.
The inventors herein have devised systems and methods to address these issues. In one example, a system for a flow cell for a hybrid flow battery, comprising: one or more electrolyte inlets; one or more electrolyte outlets; a redox plate comprising a plurality of electrolyte flow channels; conductive inserts attached to the redox plate between adjacent electrolyte flow channels; a redox electrode attached to a surface of the redox plate; a plating electrode, comprising: a plurality of folded fins with an oscillating cross-section, the plurality of folded fins comprising: a first planar surface; a second planar surface, parallel to the first planar surface; a plurality of ridges intersecting the first and second planar surfaces such that the plurality of ridges divide the first planar surface into a first plurality of strips, and divide the second planar surface into a second plurality of strips; and a membrane barrier located between the redox electrode and the plating electrode. In this way, the capacity and performance of a hybrid flow battery may be maximized, through decreasing the reaction kinetics, mass transport, and ohmic resistance losses at both the plating and redox electrodes.
In another example, a system for an electrolyte flow plate for a hybrid flow battery, comprising: a polymeric plate comprising a plurality of electrolyte flow channels; and conductive inserts attached to the polymeric plate between adjacent electrolyte flow channels. In this way, redox reactions at the bottom of the redox flow channels may be minimized, decreasing the ohmic resistance of the redox reaction.
In yet another example, a plating electrode for a battery, comprising: a plurality of folded fins with an oscillating cross-section, the plurality of folded fins comprising: a first planar surface; a second planar surface, parallel to the first planar surface; a plurality of ridges intersecting the first and second planar surfaces such that the plurality of ridges divide the first planar surface into a first plurality of strips, and divide the second planar surface into a second plurality of strips. In this way, performance losses of the battery may be minimized by increasing the reacting surface of the plating electrode.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It will be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description, which follows. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined by the claims that follow the detailed description. Further, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.